1. Field of the Invention
The present invention relates generally to the stimulus and measurement of electrical signals on microelectronic devices. Specifically, to providing the imaging of and electrical measurements on microelectronic devices for purposes that include device characterization, testing and failure analysis.
2. Background Information
The microelectronics field is a multi-billion dollar industry that is driving rapid technological advances in the design and fabrication of dense integrated circuits (IC""s). The continuing advances are increasing the speed and decreasing the size of devices fabricated on an IC, engendering a new generation of xe2x80x9cdeep sub-micronxe2x80x9d technology, whose circuit elements are substantially smaller than 0.5 xcexcm. Measuring the performance of these xe2x80x9cdeep sub-micronxe2x80x9d circuit elements (device characterization) and diagnosing the cause of failed IC""s (failure analysis) is a continual test and measurement challenge. Device characterization, diagnostics, and failure analysis of advanced microelectronics depends on the ability to stimulate and measure electrical signals at internal circuit points (nodes).
Microelectronic devices are often probed to measure signals at nodes not readily accessible through external connections. Probing has traditionally been accomplished by using a precision testing platform, known as a probe station, for mounting the device-under-test (DUT), mounting manipulators for placing the probes on circuit elements in the DUT, and providing a way to view the area to be tested, normally an optical microscope.
The probes typically include sharpened metal needles or wires to make electrical contact with the device or node of interest. These wire or needle-like structures are usually installed in an arm which allows the tip of the wire or needle to be placed in electrical contact with a particular circuit point, while avoiding contact with other electrical structures necessary to provide power and other signals to the device-under-test (DUT). This arm is often referred to as a probe and the wire or needle-like structure extending from it is known as a probe-tip.
These metal needles or wires are often located at the end of precision manipulators (probe positioners), which are used to accurately place the tip of the needle or wire on the circuit element to be measured or stimulated. Substantial effort has been expended on the design of such probe positioners, since they are used to place the probe-tip precisely on micron-size devices inside the integrated circuit and keep stable contact for many minutes or hours.
The probe manipulators are typically integrated with the probe station. The location of a circuit element of interest and of the probe-tip is determined by viewing both through an optical microscope(s) that are mounted on the probe station. During IC testing or device characterization, several such probes are typically used to probe the internal circuit, and each is placed using the common high-magnification viewing system, a probe station microscope or lens arrangement.
This traditional probe station and needle or wire probe system has sufficed for many years to stimulate and measure signals from the internal nodes of integrated circuits. However, the size of the circuit elements comprising many present day IC""s is under 0.5 xcexcm and cannot be seen using probe station optical microscopes. Under an optical microscope, even at substantial magnification, two 0.5 xcexcm devices, positioned 0.5 xcexcm apart, often cannot be resolved. Miniaturization has reduced the dimension/size of microelectronic circuit elements to the point where optical imaging systems are no longer capable of the resolution needed to place probes on the nodes of interest. Simply put, the dimensions of microelectronics have shrunk below the size that can be imaged with optical imaging systems now on probe stations. Additionally, traditional needle or wire probe tips, because of their larger tip diameter, cannot reliably make electrical contact with sub-0.5 xcexcm circuit elements. When contact can occasionally be made using traditional probe tips, the large capacitance and inductance associated with their size changes the circuit characteristics, altering the true performance of the device or circuit. This effect is known as xe2x80x9cprobe loadingxe2x80x9d or xe2x80x9cloadingxe2x80x9d of the DUT by the probe.
Users of present day probe stations often have considerable investment in their probe stations. For instance, there is also enormous investment in the software that controls and coordinates the probe stations. Traditional probe stations are well configured to stimulate devices and mechanical probes are still useful when microelectronic devices have dimensions large enough to be imaged by probe station microscope systems. For many users, replacing their current probe station is a monumental task, causing major delays in the release of new products, and engendering development expenses many times greater than the cost of a probe station.
A probe apparatus and method are described. In one embodiment, a probe apparatus includes a first positioning unit configured to be optionally added onto a probe station platform. A probe arm is attached to the first positioning unit. A second positioning unit is attached to the probe arm. A cantilever is attached to the second positioning unit. The cantilever includes a tip. The first and second positioning units are configured to position the tip over a device under test (DUT). The probe apparatus includes an electrical signal path from the tip of cantilever. The probe apparatus also includes a motion sensor configured to detect motion of the cantilever. Additional features and benefits of the present invention will become apparent from the detailed description, figures and claims set forth below.